Current therapeutics such as bisphosphonates or anabolic agents do not always effectively prevent or treat osteoporosis and inflammatory bone loss in rheumatoid arthritis, periodontitis, and implant loosening. Therefore, there is a barrier t developing effective therapeutics to preserve bone. During the 4-year parent grant award period (2007-2011), we made significant progress in delineating molecular pathways such as NFATc1 and pERK1/2 in the context of inflammatory osteolysis. In order to translate our findings into a preclinical arena, we screened several drug candidates and identified PTH(1-34) as a novel anti-inflammatory agent. Now, we are setting a new direction for our A1 competitive renewal proposal that seeks to unravel, an as yet unknown, anti-inflammatory function of PTH(1-34) in the context of inflammatory osteoclastogenesis and osteolysis. LPS has been implicated in bone infection and implant-related bone loss. LPS has been commonly used to establish a new therapeutic concept. When PTH(1-34) was delivered topically, we observed that PTH(1-34) surprisingly inhibited LPS-induced osteoclastogenesis in vivo. Subsequent experiments were conducted to investigate this phenomenon. We observed that PTH(1-34) was not inhibiting RANKL through osteoclast precursors, but was inhibiting pro-osteoclastogenic cytokines like MCSF in osteoblast cells. LPS induced phosphorylation of ERK1/2, a common inflammatory osteolysis signal transducer, was also inhibited via LPS treatment. We have optimized PTH(1-34) doses and delivery methods for the proposed experiments. Therefore, we developed a therapeutically innovative hypothesis that regionally administered low-dose PTH(1- 34) inhibits inflammatory bone loss by suppressing osteoclastogenic cytokine production in osteogenic lineage cells. We seek to investigate this hypothesis through two parallel Aims and ultimately, establish a novel anti- osteoclastogenic function of PTH(1-34). In Specific Aim 1, we will establish a novel anti-inflammatory role of PTH(1-34) in the context of osteolysis in vivo. We will determine whether regionally applied low-dose PTH(1-34) in a hydrogel prevents inflammatory osteolysis in response to clinically relevant stimuli such as RANKL, LPS and hip joint simulator generated CoCr wear particles. Osteoclastogenesis will be measured by cathepsin K optical signals and by counting osteoclast numbers. Dynamic bone histomorphometry will enable us to examine bone turnover. In Specific Aim 2, we will define the mechanism by which PTH(1-34) exhibits an anti- inflammatory effect in osteoblasts. We will examine the functional interactions between pERK/cytokine expression and two diverging PTH signaling pathways (Gs/adenylate cyclase/cAMP and Gq/11-phospholipase C). We will further delineate the functional importance of each pathway using pathway-specific analogs, our in vivo osteolysis and in vitro macrophage-osteoprogenitor co-culture models. In summary, we will provide novel therapeutic and mechanistic insights into specific anti-inflammatory function of hydrogel-based delivery of low- dose PTH in the setting of inflammatory osteolysis for drug development.